Lighting spectrum (color distribution) is very important for growing plants. Even among traditional lighting technologies, low pressure sodium lights aren't used to grow plants; even though they're more efficient than high pressure sodium, they don't have a plant-growing spectrum.

Most of the LED companies out there agree that some colors are more useful to plants than others, and many even claim that light outside of the visible range is good for growing plants. Scientific research has shown that plants primarily use colors in the visible range for photosynthesis, but that plants are also affected by light outside the visible range. Scientific research also demonstrates that the ratio (relative intensity) of different colors of light has important effects on plants.

It would be awesome if all LED vendors would list the LED wavelengths they use as well as the ratio, but at the moment this information seems to be considered something of a "special sauce" and isn't commonly shared. Some companies do give a graphical representation of their lights' spectrum, which is very useful (if it is real – some of the spectrum graphs aren't accurate).

In my opinion, the best LED grow lights have a spectrum which incorporate all of the wavelengths plants need for healthy growth, including UV and IR, and don't use mainly "white" LEDs. I know not everyone will agree with me about this, but see below for the details of my reasoning. The companies who have at least one light model that meets all of these criteria are listed in "All / Some Good" column of the table above, companies lying about their spectrum in one way or another are in the "Liars" column, and everyone else is in "The Questionable" column.

Questionable Claims

There are a few things I noticed in my research that are worth noting:

Lying by Omission?

Truth Lighting says they are Dedicated to supplying indoor growers with factual data on our actual spectrum, Truth Lighting is one of the only suppliers performing after-factory quality control on its LEDs using a professional grade spectrophotometer. Yet they don't supply any information I can find on their actual spectrum or a spectrum graph! They have replaceable modules in their lights so you can choose from "Full Spectrum", "Heavy IR/White", "Heavy Red", "Veg/Heavy UV" and &qupt;10K/Veg&qupt; modules — but as far as any actual information (beyond the name of these modules) about what spectra are in them, they provide none at all. With no information at all about what you are or aren't going to get, I wouldn't recommend buying a light from them.

Stretching the Truth?

Lush Lighting claims their light is Full Spectrum, UV to IR, and previously said Lush Lighting's products produce the most energetic photons plant's can absorb, UV light! Intense enough to turn green twist tie blue in only weeks. The twist tie discoloration method of measuring UV light seems a little suspect and not terribly scientific; I've had twist ties that change color with exposure to water. They provide no spectrum graph and they do not claim to have any actual UV LEDs (those with a peak wavelength of 10-400nm) in their light. Do they really have UV?

Clipped Spectrum Graphs

Many LED companies have graphs showing their lights' spectrum, but a lot of these graphs are clearly wrong and are "clipped".

LED diodes naturally give off slightly different colors of light on either side of their "peak" wavelength, in what is called a "normal" distribution also sometimes called a "bell curve" as it is shaped like a bell. LEDs coated with phosphors ("white" or "full-spectrum" LEDs) still have this natural "rounded" spectrum but with multiple "humps"- one for the underlying LED's, and one for the phosphors'. So when LED grow light companies post spectrums with "sharp corners" in them, it seems very fishy– there is almost no way to make a spectrum look like that with LEDs. Other methods of creating light such as discharge tubes (HID lights) can have "spikey" spectrums because of the different way they create light, but LEDs don't.

Advanced LED, Kind LED, Platinum LED and Spectrum King all have spectrum graphs on their websites which are clearly clipped and are not showing their actual spectrum. For companies claiming to be lighting and spectrum experts, this seems to show that they either have no idea what they are doing — or perhaps they are using these clipped graphs because they make it look like their light more-evenly covers the spectrum than it really does. Interestingly, all 4 companies show that they are (mis-)using the same UPRTek spectroradiometer, which isn't designed to handle bright lights. So much for these companies being lighting spectrum experts!

Pro Max Grow provides a spectrum graph with 2 unlabeled curves on it. Which is their spectrum? One curve is from ~380nm-770nm, the other from ~460nm-780nm. Perhaps we're meant to mentally add the two lines, but if so shouldn't they cover the same range? This isn't a real spectrum graph at all- they are just putting together a pretty graphic to try and sucker people into buying their extremely overpriced lights.

Spectrum Band Graph

While the number of different LED colors included in a grow light isn't the only thing you need to look at for determining if a spectrum is good, it is the only thing I can effectively put in a graph of this type.

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Ultraviolet (UV)

Based on my experience, I believe that UV light is important to include in an LED grow light spectrum. HPS has no UV, so you may not even realize what you're missing until you have grown with UV– it just seems to increase bud quality when you have it, and certainly increases pigmentation. One of the advantages LED lights have over traditional HID lighting is the ability to fine-tune the spectrum to anything you want, so I see no reason not to have UV to increase quality.

UVA vs. UVB

California Light Works' Solar Storm series are the only lights I'm comparing here that include UVB in their spectrum. They achieve this by adding fluorescent UVB bulbs (commonly called reptile bulbs) to their LED fixture. They claim UVB is important because The sun naturally contains large amounts of UVB. I think this is quite misleading because sunlight has a maximum of 0.15% (about 1/6th of 1%) of UVB; I don't consider that a "large amount". In comparison, 2.85% or more of the sunlight that gets through the atmosphere is UVA– 19 times more than UVB.

At least one plant pigment has been identified which reacts to UVB light and initiates the plant's stress response, so UVB light does trigger something in plants. However, it is unclear whether this is needed (instead of UVA) to get optimal growth or quality from your plants.

In my own past tests growing with fluorescent UV sources ("black lights" for UVA, and "reptile bulbs" which have some UVB), both kinds of UV did seem to make the plants more resinous than without UV. Plants grown under UVB seemed more stressed and damaged though, so I didn't see any benefit in using UVB instead of UVA. But, my tests were hardly scientific so all I can really say is that UVA worked better than UVB for me.

UV Lies

Spectrum King claims their lights consistently produce spectrums from 380-779nm, thus claiming to have ultraviolet in their spectrum (below 400nm). This statement is carefully worded to be technically correct but highly misleading– they have no meaningful UV in their spectrum at all. All "bare" LEDs without phosphor coatings produce photons in a normal distribution, meaning the vast majority of photons are produced within a 20-50nm of the LED's "peak wavelength". Some photons are still produced outside of this range; the further you get from the peak wavelength, the less are produced. Standard blue LEDs (including the "white" phosphor-coated blue CREE LEDs Spectrum King is using) will occasionally produce photons in the UV range, so they are technically correct. However, this UV output is less than 1/10th of 1% of their lights' output and is insignificant to your plants.

It is equally technically correct to say their light fixture is radioactive. Everything you deal with daily has a low level of radioactivity– even air, and there's air in the Spectrum King light. While this radioactivity is measureable, it is insignificant, just like the UV content of their light. So in the same way Spectrum King would probably (and rightfully so) call me a liar for saying their light is radioactive, I'm saying they're lying about having UV.

Infrared (IR)

Since 1957, science has known that giving plants near-infrared light (700 to 740nm, at least) actually increases the efficiency of photosynthesis due to the Emerson Effect. Plants will grow without near-infrared light, but since it increases photosynthetic efficiency, it seems silly not to have some in your spectrum.

White Dominant

As prices of white LEDs have dropped dramatically in the past few years– they are now cheaper than specific-color LEDs– there are more and more grow lights on the market which are composed mainly of white LEDs. Some vendors argue that their all-white LED grow lights are better than those using specific-wavelength LEDs.

The white LEDs are also 20-40% less efficient than single-color LEDs because of how they make white light with phosphors. This is fine when it's 10 or 20 watts of light in your kitchen, but the inefficiency really starts adding up when you're running hundreds of watts of LEDs in one fixture.

Including some white LEDs in a plant grow light probably makes sense, even if it is just to help you see the plants better. Even companies that use a large number of different-color LEDs include some white LEDs in their spectrum, as these help ensure some coverage of most of the visible wavelengths.

But because of the human-optimized (and not plant-optimized) spectrum and inefficiency of white LEDs, having 50% or more of your LED light in the form of white LEDs seems like you're missing out on the promise of an efficient and ideal plant spectrum. You may or may not agree, but I'd recommend a careful look at grow results from lights composed of 50% or more white LEDs.

Minimal Spectrum

Most people have heard that plants need blue light for vegetative growth and red light for flowering. It's true that plants don't veg well without enough blue and they don't flower well without enough red. From personal experience, I'm convinced that changing the color of your light from veg to flower is a bad thing if your light has enough blue and red to begin with, but I know some people might disagree with me. Still, scientific research has shown that both blue and red light are used by plants for hormonal signaling for growth regulation.

Despite this, some LED vendors have taken things to the extreme and offer all-blue veg lights, and all-red flowering lights. The all-red lights I compare here are marketed strictly as supplemental lights by all vendors that offer them, and they may be ok as a supplement to another light. Still, why buy 2 lights when you can buy 1 that does it all?

Advanced LED's Diamond Series EX-Veg lights are marketed as sole sources of light, but are only blue. While some plants will grow under all-blue lights, they won't grow as well as with a more balanced spectrum, and will undergo extreme shock when moved to a full-spectrum light, stalling out for many days while they get used to better light. If you don't believe me, by all means try it out yourself in a side-by-side test with a better-spectrum light– any plant that grows stems (i.e. not lettuce) will show the effect. If you're looking at buying one of these all-blue lights for supplementing an HPS for veg or flower, they may work well for that purpose, but as a sole source of light I'd never recommend them.

Several years ago, there were many LED lights on the market composed of just red and blue LEDs– 2 different color bands.

Apache Tech is the only company I'm reviewing that still offers lights with just one red and one blue color in their AT120RB model. While plants will grow under these lights, there's a reason the other LED vendors I'm comparing throw in other colors, even if it's just some white LEDs. Again, one of the advantages to LED lights is that you can customize the spectrum to try and excite all of the light-absorbing compounds in plants, and settling on just one red and one blue is really selling yourself short.

UVB Footnote

3% of the sunlight that makes it through our atmosphere is UV, when the sun is directly overhead in the sky. At least 95% of this is UVA, meaning that (95% of 3% = ) 2.85% of sunlight is UVA. At most, 5% of the UV light is UVB, meaning that at most (5% of 3% = ) 0.15% of sunlight is UVB. The amount of UVB that actually makes it through the atmosphere is highly dependent on cloud cover and atmospheric conditions, so UVB is usually less than 0.15% of sunlight.

California Lightworks and Hydro Grow both point to a 1987 study suggesting that only UVB light affects THC production in Cannabis Plants, but a later study showed the cellulose acetate filter used in the first study let UVB and UVA light through. Given the newer evidence, the only conclusions that can be drawn from the 1987 study are that Cannabis plants produce higher THC when exposed to a combination of UVA and UVB- but it cannot narrow down which wavelengths are responsible.

Spectrum Data for All Lights

In the table below, "?" entries in the "Actually have UV" column mean that I haven't been able to independently verify whether the lights actually include the UV they claim– yet. I just received an awesome StellarNet spectrometer which will allow me to test LEDs for spectrum claims, including UV, so if / when I get access to a light I'll now be able to verify claims. Check back soon as this column will be getting updated!

The data table is very large- you may need to scroll side-to-side as well as up and down to see the whole thing. Larger screens help! If you're only looking for one company or light model, enter the name in the search to only show those results.